The effects of an 8 Gy Y total body irradiation (TBI) on exploration and locomotion activities as well as temperature studied in C57BL6/J mice. Survival, body weight, and blood cell counts were also assessed in irradiation mice treated with placebo or interleukin (IL)-4. The efficacy of IL-4 treatment on improvement in exploration activity was evaluated. The study was carried out from 3h to 30 days following exposure. Our results showed a biphasic response to irradiation concerning the exploration activity of mice. Irradiated mice had reduced activity as early as 3h after exposure, with recovery of activity within 24h. The exploration activity again decreased 4 days after irradiation and the recovery occurred slowly after day 17. Il-4 ameliored the exploration status in mice in both phases. The locomotion activity was studied using a telemetry apparatus. A similar pattern to that of the exploration data was observed, with a minimal activity onserved between days 13 and 17. A radiation-induced hypothermia was also noticed over the same time period.